Thermosettable compositions containing liquid modifying agents such as propylene carbonate and organic polyisocyanates are known to be useful in the preparation of highly rigid articles, as taught, for example, in U.S. Pat. Nos. 4,709,002, 4,757,123, and 4,879,164. Aliphatic polyether polyols may additionally be employed in compositions of this type (see, for example, U.S. Pat. Nos. 4,731,427, 4,800,058, and 4,886,700). It is preferred that the thermosettable compositions are predominantly comprised of organic polyisocyanate since the physical properties of the cured reaction product (especially stiffness and tensile strength) are significantly diminished when the proportion of liquid modifying agent or aliphatic polyether polyol is increased. However, organic polyisocyanates are relatively high in cost. It would thus be highly desirable if the isocyanate content of the thermosettable composition could be reduced without adversely affecting the physical properties of the thermoset resin.
I have now made the unexpected and surprising discovery that an alkoxylated aromatic compound having an average hydroxyl functionality of at least about two and an aromatic content of at least about 10 percent, when used in place of an aliphatic polyether polyol, yields a thermoset article having much improved tensile and flexural strength and significantly higher stiffness. The isocyanate level in the thermosettable composition can thus be advantageously lowered without sacrificing performance.